RFR JDK-8207197: [lworld] VarHandle array support for value types

[mandy chung]

This adds the VarHandle support for array value element and extends
Unsafe::arrayBaseOffset and arrayIndexScale to return the base
and scale for a value type array.  I add some basic test for value
array access via VarHandle but will need to add more tests to
verify as a follow-up.

http://cr.openjdk.java.net/~mchung/valhalla/webrevs/8207197/webrev.00/index.html

Mandy